X-ray apparatus



March 10. 1925.

1,529 344 W. D. COOLIDGE X-RAY APPARATUS Original Filed July 1918Inventor:

William D Coolid e, by flhw 41 M His Attqvneg.

Patented Mar. 10, 1925.

UNITED STATES PATENT lorr es.

WILLIAM ID. COOLIDGE, OF SGHENECTAIDY, NEW YORK, ASSIGNOR TO GENERALELEC- TRIO COMPANY, A CORPORATION OF NEW YORK.

X-BAY APPARATUS.

Original application filed July 15, 1918, Serial No. 245,055. Patent No.1,365,688, the latter being a.

division of application Serial No. 161,892, filed April 13,1917, PatentNo. ,310,061. Divided. and

this application filed October 13, 1920. Serial No. 416,716.

To all whom it may concern:

Be it known that I, WILLIAM D. Coonm'on, a citizen of the United States,residing at Schenectady, in the county of Schenectady, State of NewYork, have invented certain new and useful Improvements in X-RayApparatus (division of my prior application Serial No. 245,055, filedJuly 15, 1918, which in turn is a division of Serial No. 161,892, filedApril 13, 1917, patented July 15, 1919, No. 1,310,061), of which thefollowing is a specification.

The present invention comprises an X-ray device having a number of novelfeatures rendering it particularly suitable for operation by people whohave little special training in the operation of X-ray apparatus.

The X-ray tube is connected directly to the secondary winding of atransformer which is designed to furnish current at voltages high enoughfor X-ray purposes, when the primary winding is supplied withalternating current of ordinary commercial voltage and frequency.

A terminal common to the X-ray tube, the main supply transformer and theoathode lighting transformer is connected to ground to reduce the dangerof electric shock. I

The novel features of my invention will be pointed out with greaterparticularity in the appended claims and more fully described in thefollowing description taken in connection with the accompanying drawing,which is a diagram illustrating a system of connections embodying myinvention.

Referring to the drawing, the X-ray tube comprises an envelope 1consisting, for example, of glass, into which are sealed a cathode 2 andan anode 3. The cathode comprises a coiled filament consisting of highlyrefractory metals, such, for example, as tungsten, and a surroundingfocusing device having a hemispherical member and a cylinder member,preferably also consisting of refractory metal, for example, molybdenumor tungsten. The cathode and the focusing member are electricallyconnected by attaching the end of the cathode to the focusing member.Two wires 5 and 6 which are connected to the focusing member, togetherwith a wire 7, which is connected to one end of the. cathode spiral, aresealed into a stem 8 of the X-ray tube. An insulating bridge piece 9maintains the wires 5, 6 and 7, spaced apart and serves to preserverigidity. A. heating current is conducted to the cathode spiral throughthe wires 6 and 7, which are connected to an external threaded terminal10 constructed similar to an incandescent lamp base. The cathode ispositioned, as by bending the wires 5, 6 and 7,or in any other way, tointercept on the focusing member, any inverse discharge taking placefrom a heated focal spot on the electrode 3 when negative with respectto the electrode 2. In this manner an inverse thermionic discharge isprevented from impinging on the opposite glass wall and injuring thetube.

The anode 3 of the X-ray tube consists preferably of wrought tungstenand is connected to an iron tube 11 carried by a glass stem of thetubular extension 12 of the X- ray tube. Connection is made to anexternal metal cap 13 provided with a ring so the electrical connectionmay be easily made.

As more fully described in my Patent No.

1,203,495, issued October 31, 1916, the X- ray tube is thoroughly freedfrom gases and exhausted to a pressure so low that conduction of energymay take place therethrough by thermionic current substantiallyindependent of gaseous ionization. The tube is solidly connectedby theconductors 14, 15, to the secondary terminals of a transformer 16. Theprimary of the transformer is connected by conductors 17 and 17 to asource of alternating current, as represented by con ductors 19 and 20.The current through the tube may be indicated by a suitable milliammeter18.

A current for maintaining the cathode filament at incandescence isfurnished by a small low voltage'transformer 21, the primary of whichmay be connected conveniently byconductors 22,. 23, to the same sourceof alternating current which supplies the main high potentialtransformer 16. In series with the conductor 23 is an adjustableresistance 24 for regulating the'cathodeheating current. The conductor15 preferably is solidly grounded as indicated in the draw-- mg.

The current through the X-ray tube depends mainly on three factors,namely, the electron emissivity of the cathode the tube design; and theimpressed voltage,

' As a very substantial drop'in voltage occurs in the mains 19, 20, whenthe tube is taking current from the/main transformer 16, means isprovided for maintaining the voltage of the filament heating currentsubstantially constant under these conditions to prevent anymaterialchange in the tern? P re re. of e cathod One y or m-v pensatingfor this drop in voltage comprises a boosting transformer the primary ofwhich is iniseries With the, primaryof the main transformer 16-and thesecondary of Whichis connected by conductors 26,27, in series with thesecondary of the transformer 21. In some cases thisboostingtransformermay be omitted.

A resistance 28 is provided which is first included in circuit by theclosure of the switch 29. This resistance maybe removed from circuitimmediately and the tubeoperateddirectly-from the, alternating-currentsource.

What I claim as new and desire to secure by Letters Patent of; theUnited'States, is: 1. An X-ray apparatus comprising the combination ofan X-ray tube havinga cathode adapted to be heated,-and an anode,

formers. p In witness whereof, I have hereunto set a source ofalternating current, a main stepup transformer h avin a primary indingconnected to said source and a secondary winding connected to theelectrodes ofsaid tube, a separate auxiliary transformer hav ing aprimary Winding connected to said source, and a secondary Windingconnected to the cathode of said tube, and a common solid groundconnection for the cathode of a d tr be t Se d re. wi d g of:

and. secondary windingconnected in series. -W th the secondary of theauxiliary-trans:

former, and afconnectionto ground common to the secondaries of my handthis 6th day of October, 1920...

WILLIAM 1). ooonmen.

said three trans.

